1. Field of the Invention
This invention relates to improvements in electric reserve batteries consisting of solid electrodes, formed for example of lead and lead dioxide, and immersed when in operation in an electrolyte producing soluble reaction products at the electrodes.
As distinct from the conventional lead-acid secondary battery in which porous electrodes are immersed in a sulphuric acid electrolyte, the electrodes of the batteries to which the present invention relates are of a dense, nonporous form, being made, for example, by electro-deposition or by casting. The electrolyte employed is preferably perchloric acid or fluoboric acid, though fluorsilicic or nitric acid may in some cases be employed.
Such a battery employing lead, lead dioxide and fluoboric acid yields an electrical potential of about 1.5 volts and many applications of such cells require that higher potentials be obtained by connecting a plurality of such cells in series.
2. Description of the Prior Art
A convenient known method of providing a battery consisting of cells of the type above described is to coat a metal, usually lead on one side of a thin, electrically conductive substrate and an oxide of the metal, usually lead dioxide, on the other. Plates made of such composite material may then be used as both electrodes and cell walls, their edges being sealed together by insulating material to form the electrolyte spaces. The end electrodes of such a battery need include respectively only the metal and the metal oxide coatings.
Batteries of the construction above described are often used as reserve batteries, the electrolyte being introduced between the plates of each cell only when the battery is required for use. It is usual to fill all the cells at the same time to avoid the production of intercell short circuits. In so doing it is difficult to avoid both over-filling and under-filling of the cells. In many applications of reserve batteries space is at a premium and this fact prohibits the use of many known exact methods of filling.
Some batteries intended for applications in which they are rotated while in use are formed with flat, parallel bi-polar plates disposed in planes perpendicular to the axis of rotation. Equalisation of the quantity of electrolyte in the cells of a battery has then been affected by providing small holes through the intermediate, bi-polar electrodes separating adjacent cells of the battery. This simplifies the filing of the cells but introduces some difficulties.